Clinical thermometers are very helpful in the diagnosis of diseases. The tympanic membrane is generally considered by the medical community to be superior to oral, rectal, or underarm sites for representing the body's internal temperature. The temperature of the tympanic membrane can be measured by detecting the infrared radiation from the tympanic membrane in the ear canal. In addition, the time needed for the body temperature measuring by using an infrared thermometer is short. The use of infrared thermometers therefore has become prevalent.
Referring to FIG. 1A, a tympanic thermometer is provided with a shutter mechanism for controlling the incoming of the infrared radiation from the tympanic membrane. When the elongated detection portion 11 is inserted into the external ear canal, the shutter mechanism is opened instantly to let the sensor 12 sense the infrared radiation in the ear canal and thereby the temperature of the tympanic membrane can be determined.
The shutter mechanism includes a base 13, a shutter plate 14, a mounting plate 15, a blocking element 16, a first linking element 17, a second linking element 18, a torsion spring 101, and a tension spring 102, wherein the base 13 is formed with a horizontal groove 131 and a vertical slot 132. The horizontal groove 131 is for mounting a wave guiding duct 103 and at the rear end of it is provided with a sensor 12. The shutter plate 14 is mounted within the vertical slot 132 of the base 13 and can be used to close the wave guiding duct 103. The mounting plate 15 is formed with a first, second, and third stubs 151, 152, 153, and a guiding portion 155. The blocking element 16 is pivotally mounted on the first stub 151. One end 161 of the blocking element 16 can prevent the shutter plate 14 from moving downward. One end of the first linking element 17 is engaged with and can only be moved horizontally in the groove 154. At the other end of the first linking element 17 is provided a push button 19 which can slide in the guiding through hole (not shown) of the guiding portion 155. The torsion spring 101 is mounted on the stub 152. One end of the torsion spring 101 is connected to the lower end of the shutter plate 14 and the other end abuts against a stub 171 formed on the linking element 17. The middle stub 181 of the second linking element 18 is telescopically engaged with the second stub 152. At one end of the second linking element 18 is provided a stub 182 pivotally connected with the first linking element 17 and at the other end is formed a snap groove 183 in which the end 162 of the blocking element 16 can be confined. One end of the tension spring 102 is connected to the third stub 153 and the other end to the first linking element 17.
With respect to the above prior art construction, referring to FIG. 1B, when the push button 19 is pressed, the first linking element 17 is moved horizontally and drives the second element 18 to pivot. In the meantime, the torsion spring 101 is twisted and accumulates energy. However, the shutter plate 14 will not move downward because it is blocked by the blocking element 16. Referring to FIG. 1C, when the second linking element 18 drives the blocking element 16 to pivot, the shutter plate 14 will be moved downward abruptly by the energy released from the torsion spring 101. When the push button 19 is released, the tension spring 102 causes the first linking element 17 to go back to its original position and the torsion spring 101 restores its original position and causes the shutter plate 14 to move upward and close the wave guiding duct 103.
The aforementioned prior art shutter construction achieves the shutter effect by means of a blocking element 16 and is provided with many parts. This incurs a high manufacturing cost.